This invention relates to systems and methods for controlling the pressure of gas in a plurality of inflatable dunnage members, such as in the form of "air mattresses", that are changeable with gas under pressure from a common control pipe and are interposed between cargo units in a freight-carrying conveyance and inflated, after loading of all cargo units, to fill the void between such cargo units and thus prevent shifting of, and damage to, said cargo units in event of shock impacts to the conveyance during transit.
It has heretofore been proposed to provide air-mattress-type dunnage members having a cargo-engageable area of approximately 9200 square inches and to inflate said dunnage members to a preselected pressure of between about 1/2 p.s.i. and 3 p.s.i., selected according to the nature of the cargo. For instance, this preselected pressure will be considerably lower for relatively light cargo units with fragile containers than for heavy cargo units such as refrigerators. If dunnage members of this area are charged with air at the preselected pressure at the loading point and no means are provided for maintaining this pressure constant, the shoring force exerted by the inflated dunnage members on the cargo units will vary 575 pounds for each ounce per square inch change in pressure in the dunnage member, will vary about 4600 pounds for each inch of mercury change in barometric pressure due either to weather changes or changes in altitude, and will vary about 1% for each 6 degrees Fahrenheit change in ambient temperature. Thus, if the air pressure in the dunnage members should increase even very slightly during transit, the cargo will be crushed, whereas if such pressure should reduce even slightly the cargo may be inadequately shored and thus be able to shift and become damaged. Such dunnage members may be utilized in cargo operations on trains, boats, trucks and aircraft.
The principal object of this invention is therefore to provide an improved control system and method for preadjusting the preselected pressure to be employed in the dunnage members and thereafter sensitively maintaining said dunnage members charged with gas at said preselected pressure irrespective of leaks and changes in ambient temperature and/or barometric pressure due to variations in weather or altitude during transit.
It is another object of the present invention to provide a control system of the aforesaid nature which can utilize pressurized air sources generally existent upon transportational conveyances.
These objects and other objects and advantages of the invention will be apparent from the following description.